Small for their age maybe?

Hi mate, they're looking good! I'm at a similar stage to you and tried to up the light. I'm using 2x p1000 for mine at 60% 18" above canopy. I can tell it's a little too much for them as they go to "sleep" a little early. The last time I increased I got some purple stems near the top. Which also confirms to much light. I'm keeping it at this to prevent too much stretch. Based on my experience and how your plants are looking (great btw!) But I can see a little purple stems so I wouldnt increase that dramatically. I'd say you're at the right range for now. Hope this helps 🙂